Device and method for substrate displacement detection

ABSTRACT

Disclosed is an apparatus and method for detecting positional displacement of a board. A board  20  having a surface formed with a conductive pattern  25  is transferred in a direction A while supplying an AC signal from a power supply section  3  to the surface of the board. The level of positional displacement of the board is detected in accordance with the transfer speed of the board and the difference between the timings of the intermediate signal levels generated when the AC signal is sensed by a pair of position sensors  1, 2  opposed to the leading edge of the board. The present invention allows positional displacement of the board to be detected in a simple non-contact structure while maintaining a high degree of accuracy without variation over time.

TECHNICAL FIELD

The present invention relates to an apparatus and method for detectingpositional displacement of a board having a surface formed with aconductive pattern, relative to a direction approximately orthogonal toa transfer direction thereof.

BACKGROUND ART

In order to inspect positional error of a board having a surface formedwith a conductive pattern, there has been known an optical or mechanicalmethod for sensing, for example, the leading edge of the board beingtransferred.

There has also been employed a method in which two pairs of sensors arelocated, respectively, at orthogonally intersecting portions of aconductive pattern formed on the surface of a board to detect positionaldisplacement of the board in accordance with the difference betweensense signals from the sensors, as disclosed in Japanese PatentLaid-Open Publication No. 10-311861.

However, the optical sensing method involves a problem of difficulty inhigh-accuracy detection due to variation in detection level caused bydeterioration in light-emitting means or changes in surroundingatmosphere. The same problem is observed in the mechanical sensingmethod.

In the method disclosed in the Japanese Patent Laid-Open Publication No.10-311861, a board is located and fixed at a given position of anapparatus for inspecting the conduction of a wiring pattern, and thenthe two pairs of sensors each having a width about one-half of the linewidth of the conductive pattern are disposed, respectively, at portionsof the conductive pattern orthogonally intersecting in the X-directionand the Y-direction. Therefore, due to the requirement of providing fourhigh-precision sensors each having a width about one-half of the linewidth of the conductive pattern, the method is limited to only aparticular application.

Thus, it is desired to achieve a board-displacement detection apparatuscapable of being arranged at a desired position on a transfer path in asimple structure while maintaining a high degree of accuracy withoutvariation over time.

It is therefore an object of the present invention to provide aboard-displacement detection apparatus and method capable of solving theabove problems, for example, capable of being arranged at a desiredposition on a transfer path in a simple structure while maintaining ahigh degree of accuracy without variation over time.

DISCLOSURE OF INVENTION

In order to achieve the above object, according to a first aspect of thepresent invention, there is provided an apparatus for detectingpositional displacement of a board having a surface formed with aconductive pattern, relative to a direction orthogonal to a transferdirection thereof. The apparatus comprises: at least two pattern-edgesensing means disposed, respectively, at predetermined arrival positionswhich are spaced apart from each other at a given distance and to bealigned with the leading edge of the conductive pattern locateddownstream relative to the transfer direction, and adapted to becapacitively coupled with the conductive pattern in a non-contactmanner; signal supply means for supplying an AC signal from a givenportion of the conductive pattern other than the leading edge to theleading edge; and displacement determination means for sensing thedifference between respective timings when the AC signal supplied fromthe signal supply means is sensed by the pattern-edge sensing means todetermine the positional displacement of the board transferred to thepredetermined arrival positions. The signal supply means is operable tosupply the AC signal at least at the time when the leading edge of theconductive pattern arrives at the predetermined arrival positions, andthe displacement determination means is operable to determine the levelof inclination of the board in accordance with the level of differencebetween the sense signals.

In the above apparatus, the displacement determination means may beoperable to sense the respective arrival positions of the leading edgeto the pattern-edge sensing means, in accordance with the positions ofthe respective approximately intermediate levels between the minimum andmaximum levels in the sense signals from the pattern-edge sensing means,to determine the inclination relative to the line between the positionsof the pattern-edge sensing means and the displacement relative to thetransfer direction, in accordance with the difference between the sensesignals from the pattern-edge sensing means.

The signal supply means may include capacitive coupling means forsupplying the AC signal to the given portion of the conductive patternin a non-contact manner.

The board may be a board for a liquid-crystal display panel. In thiscase, the conductive pattern may be an indium tin oxide film or analuminum film. Further, the board for a liquid-crystal display panel maybe made of glass or plastic.

According to a second aspect of the present invention, there is provideda method for detecting positional displacement of a board having asurface formed with a conductive pattern, relative to a directionorthogonal to a transfer direction thereof. The method comprises thesteps of: providing at least two pattern-edge sensing means disposed,respectively, at predetermined arrival positions which are spaced apartfrom each other at a given distance and to be aligned with the leadingedge of the conductive pattern located downstream relative to thetransfer direction, and adapted to be capacitively coupled with theconductive pattern in a non-contact manner; supplying an AC signal tothe conductive pattern; sensing the AC signal supplied to the conductivepattern of the board transferred to the predetermined arrival positions,through the pattern-edge sensing means; and detecting the differencebetween respective timings when the AC signal is sensed by thepattern-edge sensing means to determine the positional displacement ofthe board transferred to the predetermined arrival positions.

In the above method, the detecting step may include detecting therespective arrival positions of the leading edge to the pattern-edgesensing means, in accordance with the positions of the respectiveapproximately intermediate levels between the minimum and maximum levelsin the sense signals from the pattern-edge sensing means, to determinethe inclination relative to the line between the positions of thepattern-edge sensing means and the displacement relative to the transferdirection, in accordance with the difference between the sense signalsfrom the pattern-edge sensing means.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram of the principle of detectingpositional displacement of a board in a board-displacement detectionapparatus according to one embodiment of the present invention.

FIG. 2 is an explanatory flowchart of a control for detecting positionaldisplacement of a board in the board-displacement detection apparatusaccording to the embodiment.

FIG. 3 is an explanatory diagram of the principle of detectingpositional displacement of a board by position sensors 1, 2 according tothe embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, one embodiment of the present inventionwill now be described in detail. The following description will be madein conjunction with a circuit-pattern inspection apparatus forinspecting the quality of a dot matrix pattern of a dot matrix displaypanel before being assembled as a dot matrix liquid-crystal display.However, the present invention is not limited to such a pattern, but maybe applied to any pattern with one end having a plurality of wiringpatterns allowing a common sensor to be arranged such that it iscapacitively coupled commonly with respective wiring pattern groups atdifferent positions.

In this embodiment, the board-displacement detection apparatus comprisesan XYZθ transfer table 30. The XYZθ transfer table 30 can be controlledto 3-dimensionally move a board to be inspected while holding it on thesurface thereof and set the board at any position. In an operation ofdetecting positional displacement of the board, a board 20 having asurface formed with a conductive pattern 25 is held on the XYZθ transfertable 30 controlled to transfer the board, for example, in a directionindicated by the arrow A, and the board-displacement detection apparatusis operable to detect positional displacement of the board 20 relativeto a direction approximately orthogonal to the transfer direction A.

In this embodiment, the board 20 is a board for a liquid-crystal displaypanel, and made of glass. Specifically, the glass board 20 has a surfaceformed with the conductive pattern 25.

However, the material of the board in present invention is not limitedto glass, but any other suitable material having an equivalent functionmay be used. For example, the board may be made of plastic. The plasticboard can achieve the same function as that of the glass board, andreduce the risk of breakage as compared to the glass board. Thus, if theplastic board is used as a substitute for the glass substrate, theinspection can be carried out in the same way without any modificationin an after-mentioned control and others.

Preferably, the conductive pattern to be used for detection is formed onthe surface of the board 20 to extend in a direction orthogonal to thetransfer direction of the board instead of in a direction parallelthereto.

The XYZθ transfer table 30 can be moved not only in the arrow directionA but also in a direction orthogonal to the arrow direction A. Thus,positional displacement of the board relative to a direction parallel tothe arrow direction A can be detected by changing the moving directionof the XYZθ transfer table 30 or the transfer direction of the board 20,and the positions of after-mentioned position sensors.

In this embodiment, even if the conductive pattern is arranged in anydirection except for a direction parallel to the transfer direction ofthe board, positional displacement of the board can be detected byappropriately changing the positions of after-mentioned positionsensors. The following description will be made by taking an indium tinoxide (ITO) film as an example of the conductive pattern.

The board-displacement detection apparatus according to this embodimentincludes two position sensors 1, 2 serving as pattern-edge sensing meansdisposed, respectively, at two predetermined arrival positions which arespaced apart from one another at a given distance and to be aligned withthe leading edge 25 a of the conductive pattern 25 located downstreamrelative to the transfer direction, and adapted to be capacitivelycoupled with the conductive pattern in a non-contact manner. Theboard-displacement detection apparatus also includes a power supplysection 3 serving as signal supply means for supplying an AC signal froma given portion of the conductive pattern 25 located upstream relativeto the transfer direction to the leading edge 25 a of the conductivepattern 25. The position sensors 1, 2 and the power supply section 3 arefixedly attached on a sensor panel (not shown) while locating theirouter surfaces in one plane.

The position sensors 1, 2 are formed as conductive flat plates havingapproximately the same area, and the power supply section 3 is alsoformed as a conductive flat plate. Thus, even if the power supplysection 3 is not in contact with the conductive pattern 25 on thesurface of the board 20, an AC signal with a certain level of highfrequency can be supply to the power supply section 3 whileappropriately setting the distance between the surface of the board 20and the conductive pattern 25 so as to form a capacitive couplingtherebetween to allow the AC signal to be supplied to the conductivepattern 25 of the board 20 through the power supply section 3.

For this purpose, the power supply section 3 is connected with a signalgenerator 14 including an oscillation circuit operable to oscillate at agiven frequency, and supplied with an AC signal with the given frequencyoscillated by the oscillation circuit.

Then, when the conductive pattern 25 arrives at a position facing to theposition sensors 1, 2, a conduction path is formed between the powersupply section 3 and the position sensors 1, 2 through the conductivepattern 25 to send the AC signal from the power supply section 3 to anamplifier circuit 12 through the position sensors 1, 2. Then, an A/Dconverter circuit 13 converts the amplified sense signals from theamplifier circuit 12 into corresponding digital signals, and a controlsection 11 takes in the digital signals so as to detect the timings whenthe AC signal is sensed by the position sensors 1, 2 to determinepositional displacement of the board 20.

In the apparatus according to this embodiment illustrated in FIG. 1, theposition sensors 1, 2 are disposed, respectively, at positions wherethey can sense the AC signal at the same timing when the board 20 istransferred without any positional displacement. This means thatpositional displacement of the board 20 is proportional to the level ofdifference between the respective sense signals of the sensors 1, 2.

However, the present invention is not limited to the above arrangement.For example, even in case where the AC signal is not sensed at the sametiming when the board 20 is transferred without any positionaldisplacement, if the level of difference between the respective sensesignals of the position sensors 1, 2 is clarified in advance, thepositional error of the board 20 can be recognized in accordance withthe level of difference between the respective sense signals. Thus, infundamentally the same way as that in the above embodiment, the level ofpositional displacement of the board 20 can be determined in accordancewith the change between the timings of sensing the AC signal by theposition sensors 1, 2 when the board 20 is transferred under a presetcondition of no positional displacement and actual timings of sensingthe AC signal by the position sensors 1, 2 when the board 20 istransferred under an unknown condition.

The position sensors 1, 2 serving as pattern-edge sensing meansdisposed, respectively, at two predetermined arrival positions which arespaced apart from one another at a given distance and to be aligned withthe leading edge 25 a of the conductive pattern 25 located downstreamrelative to the transfer direction, and adapted to be capacitivelycoupled with the conductive pattern in a non-contact manner, and thepower supply section 3 serving as signal supply means for supplying anAC signal from a given portion of the conductive pattern 25 locatedupstream relative to the transfer direction to the leading edge 25 a ofthe conductive pattern 25 are fixedly attached on the sensor panel (notshown) while locating their outer surfaces in one plane.

That is, the position sensors 1, 2 are disposed, respectively, atpositions where they can sense the AC signal at the same timing when theboard 20 is transferred without any positional displacement. This meansthat positional displacement of the board 20 is proportional to thelevel of difference between the respective sense signals of the sensors1, 2.

However, the present invention is not limited to the above arrangement.For example, even in case where the AC signal is not sensed at the sametiming when the board 20 is transferred without any positionaldisplacement, if the level of difference between the respective sensesignals of the position sensors 1, 2 is clarified in advance, thepositional error of the board 20 can be recognized in accordance withthe level of difference between the respective sense signals. Thus, infundamentally the same way as that in the above embodiment, the level ofpositional displacement of the board 20 can be determined in accordancewith the change between the timings of sensing the AC signal by theposition sensors 1, 2 when the board 20 is transferred under a presetcondition of no positional displacement and actual timings of sensingthe AC signal by the position sensors 1, 2 when the board 20 istransferred under an unknown condition.

A control for detecting positional displacement of the board in theboard-displacement detection apparatus according to the above embodimentwill be described with reference to FIG. 2 which is an explanatoryflowchart of the control.

In this embodiment, the board-displacement detection apparatus islocated upstream of a board transfer path relative to a board inspectionapparatus for inspecting the quality of the pattern of a board or thelike to supply the board without positional displacement.

At Step S1, a board to be inspected is set on the transfer path, andtransferred toward the board-displacement detection apparatus. At StepS2, it is checked whether the board arrives at the position of the XYZθtransfer table 30 of the board-displacement detection apparatus. If theboard has not arrived at the position of the XYZθ transfer table 30, theprocess will return to Step S1 to continue the transfer.

When the arrival of the board to the position of the XYZθ transfer table30 is confirmed in Step S2, the process advances to Step S3, and theboard is positioned and held on the XYZθ transfer table 30.

Subsequently, at Step S4, the XYZθ transfer table 30 is controlled toset the board 20 at an initial position for allowing the positionsensors 1, 2 and the power supply section 3 to be capacitively coupledwith the conductive pattern in an operation of actually detectingpositional displacement of the board. This initial position is set at aposition where the positional sensors 1, 2 generate no sense signal(un-sensed position). Through the above Steps, the preparation for theboard-displacement detecting operation has been completed. Then, at StepS5, the control section 11 activates the signal generator 14 to supplyan AC signal (supply power) to the power supply section 3.

Subsequently, at Step S6, the XYZθ transfer table 30 is moved in theY-direction (the arrow direction A in FIG. 1) at a constant speed.Simultaneously, at Step S7, the control section 11 drives the amplifier12 and activates the A/D converter circuit 13 to convert the respectiveoutputs of the position sensors 1, 2 into corresponding digital signals,and takes in the digital signals.

Then, Step S8, after the outputs of the position sensors 1, 2 arechanged from the un-sensed state to a sensed state, it is monitoredwhether the outputs are saturated. If both outputs of the positionsensors 1, 2 are not saturated, the process will return to Step S6 tocontinue the monitoring of the transfer of the board and the outputs ofthe position sensors 1, 2.

When the saturation of both outputs of the position sensors 1, 2 isconfirmed in Step S8, the process advances to Step S9, and the levels ofthe sense signals of the position sensors 1, 2 are compared with oneanother. Specifically, for each of the sense signal levels, the signaloutput level at no output of any sense signal and the signal outputlevel at the saturation of the output are compared with one another todetermine the timing of the output of an approximately intermediatesignal level. Then, the respective timings of sensing the intermediatesignal levels in the position sensors 1, 2 are compared to detect whichoutputs of the position sensors is how much earlier, or the timedifference between the respective timings of outputting the intermediatesignal levels of the position sensors 1, 2.

Subsequently, Step S10, the level of positional displacement of theboard is determined in accordance with the level of the time difference.In this embodiment, the AC signal is continuously supplied from thepower supply section 3 to the conductive pattern formed on the surfaceof the board. Thus, the outputs of the position sensors 1, 2 as theresult of sensing the AC signal from the power supply section 3 areincreased as the conductive pattern gets close to the position sensors1, 2. When the conductive pattern is fully aligned with the positions ofthe position sensors 1, 2, the level of the sense signal is maximizedand saturated. Then, when the leading edge of the conductive pattern islocated directly below the position sensors 1, 2 (directly below at thecenter of each of the position sensors because each has asymmetrical/diphycercal shape), each output of the sense signals has theintermediate level.

As above, since the difference between the sensing timings of theposition sensors 1, 2 is proportion to positional displacement of theboard, the time difference between the sensing timings of the positionsensors 1, 2 are detected at Step S10 to determine the level ofpositional displacement of the board.

The processing of detecting the positional displacement in the aboveembodiment will be described in more detail with reference to FIG. 3which is an explanatory view of the principle of detecting positionaldisplacement of the board by the position sensors 1, 2 in theembodiment.

As shown in FIG. 3, the conductive pattern 25 is formed on the surfaceof the board 20. The power supply section 3 arrives at the position ofthe pattern 25 before the position sensors 1, 2 arrive at the positionof the pattern 25, and the AC signal is continuously supplied to thepower supply section 3 from Step S5.

Thus, when the XYZθ transfer table is moved in the arrow direction A,the conductive pattern 25 arrives at a position opposed to the sensors1, 2, and the opposed area is gradually increased. When the conductivepattern is moved at a position fully opposed to the position sensors 1,2, the sensing outputs of the position sensors 1, 2 are saturated. Thisstate is shown at the bottom of FIG. 3.

If each of the position sensors 1, 2 is formed in a symmetrical shape inboth the moving or transfer direction and the lateral direction, theposition of the intermediate level of the sense signal will correspondto the state when the conductive pattern has been moved just tointermediate (center) positions of the position sensors 1, 2. Thus, theleading edge of the conductive pattern on the surface of the board canbe accurately detected.

Then, the levels of sense signals of the position sensors 1, 2 arecompared with one another to detect the difference x between the timingsof the intermediate levels, and the difference x can be compared withthe moving speed of the board 20 to detect the level of positionaldisplacement of the board.

In addition, the above detecting operation can be performed completelyin a non-contact manner. Thus, the level of the sense signal isproportional to the area of the conductive pattern opposed to theposition sensor, and positional displacement of the board can bedetected with an extremely high degree of accuracy.

Particularly, instead of using the absolute values of the sense signalsas a reference value of the detection, the aforementioned embodiment isdesigned to detect the difference based on the relative comparison ofthe output signals of the position sensors 1, 2. Thus, a highly reliabledetection result can be obtained without any adverse affects fromdeterioration or variation over time in the performance of the controlsection, the detection circuits 12, 13 and/or the signal generator 14.

Then, at Step S11, the XYZθ transfer table 30 is controlled to correctthe displacement of the board so as to allow the board to be set at anaccurate position. Then, at Step S15, the accurately positioned boardcan be subjected to the quality inspection. After the inspection, thisprocessing will be competed.

Even if a plurality of boards are simultaneously mounted on the XYZθtransfer table 30, the above highly accurate displacement detectionallows positional displacements in all of the boards to be accuratelycorrected by only one cycle of the board-displacement detectingoperation.

While the ITO pattern has been used as the conductive pattern in theabove embodiment, any type of conductive patterns may be used withoutany restriction if the opposed regions between the power supply section3, the position sensors 1, 2 and the conductive pattern are connectedwith AC power.

For example, it is to be understood that the conductive pattern may beformed of an aluminum film as a substitute for the ITO film to performthe detecting operation in the same way. The difference in the materialof the conductive pattern has little impact on the detecting, and anymaterial may be used to perform the detecting operation in the same way.For example, copper, silver or gold may also be used.

Further, the embodiment illustrated in FIGS. 1 and 3 has employed thesingle power supply section 3. However, if the conductive patternopposed to the position sensors 1, 2 is composed of two independentconductive pattern groups, the power supply section may be divided intotwo to supply power to the conductive pattern groups opposed to thecorresponding position sensors 1, 2, separately.

The above embodiment is designed to detect the relative differencebetween the sense signals of the position sensors 1, 2. Thus, the powersupply section is limited to the shape illustrated in FIG. 1 or 3, butmay be formed in any shape. Further, instead of the non-contact type,probe-shaped power supply sections may be brought into direct contactwith the conductive pattern to supply an AC signal thereto.

Moreover, the above embodiment is not designed to compare the absolutevalues of the sense signals so as to determine positional displacementof the board. Thus, there is no need for controlling the distancebetween the sensors and the conductive pattern strictly and accurately,and the control for setting the initial position at Step S4 can beperformed without difficulties.

If it is desired to accurately control this distance, the followingoperation may be performed. The board is held by the XYZθ transfer table30, and then the XYZθ transfer table 30 is once lifted toward the sensorpanel. Then, it is checked whether the surface of the board 20 is incontact with the sensor panel. If the surface of the board is not incontact with the sensor panel, the XYZθ transfer table 30 is furtherlifted.

When the surface of the board 20 is in contact with the sensor panel,the XYZθ transfer table 30 is moved downward at a given distance. Inthis manner, the distance between the position sensor 1, 2, the powersupply section 3 and the conductive pattern on the surface of the boardmay be accurately controlled. Further, the position sensor 1, 2 and thepower supply section 3 can be capacitively coupled with the conductivepattern in a non contact manner, and the level of sense signal can becontrolled in a given range.

INDUSTRIAL APPLICABILITY

As mentioned above, according to the present invention, instead of usingthe absolute values of sense signals in the board-positionaldisplacement detecting operation, the level of positional displacementis detected in accordance with the relative comparison of the outputsignals from the pattern-edge sensing means. Thus, a highly reliableresult of board-displacement detection can be obtained in a simplestructure without any adverse affects from deterioration or variationover time in the performance of associated components.

1. An apparatus for detecting positional displacement of a board havinga surface formed with a conductive pattern, relative to a directionorthogonal to a transfer direction thereof, said board, said apparatuscomprising: at least two pattern-edge sensing means disposed,respectively, at predetermined arrival positions which are spaced apartfrom each other at a given distance and to be aligned with the leadingedge of said conductive pattern located downstream relative to saidtransfer direction, and adapted to be capacitively coupled with saidconductive pattern in a non-contact manner; signal supply means forsupplying an AC signal from a given portion of said conductive patternother than said leading edge to said leading edge; and displacementdetermination means for detecting the difference between respectivetimings when said AC signal supplied from said signal supply means issensed by said pattern-edge sensing means, to determine the positionaldisplacement of said board transferred to said predetermined arrivalpositions, wherein said signal supply means is operable to supply saidAC signal at least at the time when said leading edge of said conductivepattern arrives at said predetermined arrival positions, and saiddisplacement determination means is operable to determine the level ofinclination of said board in accordance with the level of the differencebetween said sense signals.
 2. The apparatus as defined in claim 1,wherein said displacement determination means is operable to detect therespective arrival positions of said leading edge to said pattern-edgesensing means, in accordance with the positions of the respectiveapproximately intermediate levels between the minimum and maximum levelsin said sense signals from said pattern-edge sensing means, to determinethe inclination relative to the line between the positions of saidpattern-edge sensing means and the displacement relative to saidtransfer direction, in accordance with the difference between said sensesignals from said pattern-edge sensing means.
 3. The apparatus asdefined in claim 1 or 2, wherein said signal supply means includescapacitive coupling means for supplying said AC signal to said givenportion of said conductive pattern in a non-contact manner.
 4. Theapparatus as defined in claim 1 or 2, wherein said board is a board fora liquid-crystal display panel, and said conductive pattern is an indiumtin oxide film.
 5. The apparatus as defined in claim 1 or 2, whereinsaid board is a board for a liquid-crystal display panel, and saidconductive pattern is an aluminum film.
 6. The apparatus as defined inclaim 4, wherein said board is made of glass or plastic.
 7. A method fordetecting positional displacement of a board having a surface formedwith a conductive pattern, relative to a direction orthogonal to atransfer direction thereof, said method comprising the steps of:providing at least two pattern-edge sensing means disposed,respectively, at predetermined arrival positions which are spaced apartfrom each other at a given distance and to be aligned with the leadingedge of said conductive pattern located downstream relative to saidtransfer direction, and adapted to be capacitively coupled with saidconductive pattern in a non-contact manner; supplying an AC signal tosaid conductive pattern; sensing said AC signal supplied to saidconductive pattern of said board transferred to said predeterminedarrival positions, through said pattern-edge sensing means; anddetecting the difference between respective timings when said AC signalis sensed by said pattern-edge sensing means to determine the positionaldisplacement of said board transferred to said predetermined arrivalpositions.
 8. The method as defined in claim 7, wherein said detectingstep includes detecting the respective arrival positions of said leadingedge to said pattern-edge sensing means, in accordance with thepositions of the respective approximately intermediate levels betweenthe minimum and maximum levels in said sense signals from saidpattern-edge sensing means, to determine the inclination relative to theline between the positions of said pattern-edge sensing means and thedisplacement relative to said transfer direction, in accordance with thedifference between said sense signals from said pattern-edge sensingmeans.
 9. The method as defined in claim 7 or 8, wherein said supplyingstep includes supplying said AC signal to said conductive patternthrough capacitive coupling means in a non-contact manner.
 10. Theapparatus as defined in claim 5, wherein said board is made of glass orplastic.